STOCKTON, Tooele County -- Workers at the Army's chemical weapons incinerator near here began a sampling program this month that will help determine the order in which bulk containers of mustard agent will be destroyed.

The project is complicated by the fact that some of the mustard containers have mercury contamination and some have solidified material called a "heel."

Mercury, a toxic element, is vaporized by incineration but is not destroyed.

The sampling project should take two to three years, according to a press release from Alaine Southwest of Deseret Chemical Depot, where the material is stored. "Bulk container disposal operations are expected to begin this summer, targeting for destruction sampled containers identified as having no or low mercury contamination and low solids content," the release adds.

About 6,400 bulk containers of the agent are stored at the depot, which is 60 miles southwest of Salt Lake City.